Put another way, a Salvadorean man with a high-school education needs only to come to the U.S. to increase his annual earning power more than eightfold, from $2,700 to $22,611—a figure, by the way, almost identical to the earning potential for Americans with the same level of education.

Workers at the Grasberg mining complex operated by the U.S. giant Freeport-McMoran began a monthlong strike Sept. 15, demanding at least an eightfold increase in the minimum wage, currently $1.50 an hour.